Process for producing taurine from alkali taurinates

ABSTRACT

A process for producing taurine from alkali ditaurinate or alkali tritaurinate, or their mixture, comprising the conversion of alkali ditaurinate to dialkali ditaurinate or alkali tritaurinate to trialkali tritaurinate, or their mixture, the ammonolysis reaction of ammonia added to a solution of dialkali ditaurinate or trialkali tritaurinate, or their mixture, to yield alkali taurinate, removing excess ammonia from the foregoing and neutralizing alkali taurinates with an acid to form a crystalline suspension of taurine, and recovering taurine by means of solid-liquid separation.

More than one reissue application has been filed for U.S. Pat. No.9,428,450, including U.S. application Ser. No. 16/843,272, filed Apr. 2,2020, as well as U.S. application Ser. No. 16/854,395, filed Apr. 21,2020, as well as U.S. application Ser. No. 16/854,406, filed Apr. 21,2020. Each reissue application is a reissue application of U.S. Pat. No.9,428,450.

TECHNICAL FIELD

The present invention relates to a cyclic process for the production oftaurine from alkali isethionate and from alkali vinyl sulfonate in ahigh overall yield, i.e., greater than 90%, in particular, greater than95%, by continuously converting the byproducts of the ammonolysisreaction, alkali ditaurinate and alkali tritaurinate, to alkalitaurinate.

BACKGROUND OF THE INVENTION

Taurine can be referred to as 2-aminoethanesulfonic acid and is one ofthe amino sulfonic acids found in the tissues of many animals. Taurineis an extremely useful compound because it has such pharmacologicaleffects as detoxification effect, fatigue-relieving effect andnourishing and tonifying effect. As a result, taurine finds wideapplications as an essential ingredient for human and animal nutrition.

Taurine is currently produced in an amount of over 50,000 tons per yearfrom ethylene oxide and monoethanolamine. At present time, most of thetaurine is produced from ethylene oxide, following a three-step process:(1) the addition reaction of ethylene oxide with sodium bisulfite toyield sodium isethionate; (2) the ammonolysis of sodium isethionate toyield sodium taurinate; (3) the neutralization with an acid, i.e,hydrochloric acid and, preferably, sulfuric acid, to generate taurineand inorganic salts.

Although the ethylene oxide process is well established and widelypracticed in commercial production, the overall yield is not very high,less than 80%. Moreover, the process generates a large amount of wastestream that is increasingly difficult to dispose of.

The first stage of the ethylene oxide process, the addition reaction ofethylene oxide with sodium bisulfate, is known to yield sodiumisethionate in high yield, practically quantitative, as disclosed inU.S. Pat. No. 2,820,818 under specified conditions.

Therefore, the problems encountered in the production of taurine fromthe ethylene oxide process arise from the ammonolysis of sodiumisethionate and from the separation of taurine from sodium sulfate.

According to the copending applications U.S. Ser. No. 13/999,203 andU.S. Ser. No. 13/999,439, these same issues are also encountered in theproduction of taurine from ethanol and ethylene, respectively. Sodiumisethionate is a key common intermediate and the ammonolysis of sodiumisethionate is an important step in the ethanol and ethylene processes.

U.S. Pat. No. 1,932,907 discloses that sodium taurinate is obtained in ayield of 80%, when sodium isethionate undergoes ammonolysis reaction ina molar ratio of 1:6.8 for 2 hrs at 240 to 250° C. U.S. Pat. No.1,999,614 describes the use of catalysts, i.e., sodium sulfate, sodiumsulfite, and sodium carbonate, in the ammonolysis reaction. A mixture ofsodium taurinate and sodium ditaurinate is obtained in a yield as highas 97%. However, the percentage for sodium taurinate and sodiumditaurinate in the mixture is not specified.

DD 219 023 describes detailed results on the product distribution of theammonolysis reaction of sodium isethionate. When sodium isethionateundergoes the ammonolysis reaction with 25% aqueous ammonia in a molarratio of 1:9 at about 280° C. for 45 minutes in the presence of sodiumsulfate and sodium hydroxide as catalyst, the reaction products comprise71% of sodium taurinate and 29% of sodium di- and tri-taurinate.

WO 01/77071 is directed to a process for the preparation of ditaurine byheating an aqueous solution of sodium taurinate at a temperature of 210°C. in the presence of a reaction medium. A mixture of sodium taurinateand sodium ditaurinate is obtained.

From these prior arts, it is therefore concluded that the ammonolysis ofsodium isethionate invariably yields a mixture of sodium taurinate,sodium ditaurinate, and sodium tritaurinate. The percentage yield ofsodium taurinate has not been more than 80%.

In order to obtain taurine from sodium taurinate, U.S. Pat. No.2,693,488 discloses a method of using ion exchange resins, firststrongly acid ion exchange resin in hydrogen form, then an anionexchange resin in basic form. This process is complicated and requiresthe use of large quantity of acid and base to regenerate the ionexchange resins in each production cycle.

On the other hand, CN101508657, CN101508658, CN101508659, andCN101486669 describe a method of using sulfuric acid to neutralizesodium taurinate to obtain a solution of taurine and sodium sulfate.Crude taurine is easily obtained by filtration from a crystallinesuspension of taurine after cooling. However, the waste mother liquorstill contains taurine, sodium sulfate, and other unspecified organicimpurities. It is desirable to have available a process for furtherseparation of these components to achieve an economical process and toreduce the disposal of waste stream.

It is, therefore, an object of the present invention to disclose acyclic process for the production of taurine from alkali isethionate andfrom alkali vinyl sulfonate in a high overall yield, i.e., greater than90%, in particular, greater than 95%. According to the process in thepresent invention, sodium ditaurinate and sodium tritaurinate,byproducts from the ammonolysis of sodium isethionate or sodium vinylsulfonate, are continuously converted to sodium taurinate in theammonolysis stage.

It is another object of the present invention to disclose a process forthe preparation of pure sodium ditaurinate and pure sodium tritaurinate,and their conversion to sodium taurinate. When sodium ditaurinate andsodium tritaurinate are reacted with aqueous ammonia under ammonolysisreaction conditions, a mixture of similar compositions of sodiumtaurinate, ditaurinate, and tritaurinate is formed in an equilibriumstate. This novel finding renders the cyclic process possible.

It is a further object of the present invention to disclose a processfor the complete separation of taurine and sodium sulfate from eachother and from the byproducts, i.e., sodium ditaurinate and sodiumtritaurinate. According to the process in the present invention, theresidual taurine and sodium sulfate are separated from sodiumditaurinate and sodium tritaurinate by a process of co-crystallizationof taurine and Glauber's salt at a temperature from 0 to 20° C. Thecrystalline mixture of taurine and sodium sulfate is then separated fromeach other, while the mother liquor, consisting of taurine, monosodiumditaurinate, and monosodium tritauriante, is suitable for recycling tothe ammonolysis step to prepare sodium taurinate.

DESCRIPTION OF THE DRAWINGS

FIG. 1. Schematic flowchart for the cyclic production of taurine fromsodium isethionate and sodium vinyl sulfate.

FIG. 2. Solubility curves for taurine and sodium sulfate in water.

DESCRIPTION OF THE INVENTION

The present invention relates to a cyclic process for the production oftaurine from alkali isethionate, which is a key intermediate for theethylene oxide, ethanol, and ethylene processes. This cyclic process isalso applied to the production of taurine from alkali vinyl sulfonate,another intermediate for the ethanol and ethylene processes.

For the production of taurine, sodium isethionate and sodium vinylsulfonate are preferably used, but other alkali metals, i.e., lithium,potassium, and cesium, are equally suitable. In the drawings andfollowing description, only sodium is used in replace of alkali metalsto describe the process.

In order to achieve the cyclic process, the present invention disclosesa novel finding and process for converting sodium ditaurinate and sodiumtritaurinate, byproducts of the ammonolysis of sodium isethionate, tosodium taurinate under the ammonolysis conditions. According to thecyclic process in the present invention, sodium isethionate and sodiumvinyl sulfonate are converted to sodium taurinate in a practicallyquantitative yield. A complete separation of taurine with sodium sulfateaccording to the process in the present invention ensures that taurineis obtained in high yield, i.e., greater than 90%, in particular greaterthan 95% on the basis of sodium isethionate or sodium vinyl sulfonate.

Although sodium ditaurinate and sodium tritaurinate are mentioned in theprior arts, preparation of pure products is not known. The presentinvention describes a method for the preparation of pure sodiumditaurinate and pure sodium tritaurinate from diethanolamine andtriethanolamine, respectively.

To prepare sodium ditaurinate, diethanolamine is first reacted withexcess thionyl chloride to form bis(2-chloroethyl)amine hydrochloride inquantitative yield, which undergoes sulfonation with sodium sulfite toyield the expected product. When triethanolamine is used in the samesequence of reactions, tris(2-chloroethyl)amine hydrochloride isobtained as an intermediate, disodium tritaurinate is obtained as anaqueous solution, along with sodium chloride. The reaction schemes areas follows:

When sodium ditaurinate and sodium tritaurinate are subjected to theammonolysis reaction in aqueous ammonia under the same conditions at atemperature of 220° C. for 2 hours, a mixture of similar compositions,i.e., sodium taurinate (74%), sodium ditaurinate (23%), and sodiumtritaurinate (3%), is obtained. Clearly, an equilibrium state is reachedamong the three taurinates, irrespective of the starting materials.

This novel finding renders possible the cyclic process for preparingtaurine from sodium isethionate and from sodium vinyl sulfonate, becausethe inevitable byproducts of the ammonolysis step, i.e., sodiumditaurinate and sodium tritaurinate, can be continuously converted tosodium taurinate in each successive cycle.

FIG. 1 describes the detailed unit operations for the cyclic process forthe production and isolation of taurine from sodium isethionate. Thecycle is equally applicable for the production of taurine from sodiumvinyl sulfonate.

The cyclic process starts from the ammonolysis of sodium isethionate orsodium vinyl sulfonate in aqueous ammonia at a temperature of 150 to270° C. under a pressure from the autogenous to 260 bars, andoptionally, in the presence of catalysts. Usually, catalysts are thealkaline salts of sodium, potassium and lithium. Such salts are sodiumhydroxide, potassium hydroxide, lithium hydroxide, sodium carbonate,potassium carbonate, lithium carbonate, sodium sulfate, sodium sulfite,potassium sulfate, potassium sulfite. Any one or a combination of two ormore these salts can be used as catalyst to influence the reaction.

After the ammonolysis reaction, the excess ammonia are dispelled fromthe reaction solution and reclaimed for reuse. Sodium taurinate isobtained, along with sodium ditaurinate, sodium tritaurinate, andunreacted sodium isethionate.

The strongly basic solution is neutralized with sulfuric acid to pH 5-7to yield mainly taurine, sodium sulfate, sodium ditaurinate, and sodiumtritaurinate. The content of taurine and sodium sulfate is in a molarratio of 1:0.5 to 1:0.6, and nearly the same in terms of their weight.

The initial solution is optionally concentrated, then cooled to 28 to35° C., to crystallize taurine. The first batch of crude taurine isobtained by filtration, while sodium sulfate remains in solution. Lowertemperature is to be avoided to prevent the crystallization of sodiumsulfate.

It is important to point out that sodium sulfate has the maximumsolubility at a temperature of 33° C. as shown in FIG. 2. The solubilityof sodium sulfate decreases slightly from 33 to 100° C., but drasticallyfrom 33 to 0° C. Moreover, sodium sulfate crystallizes as anhydrous formabove 40° C., but as Glauber's salt, i.e., sodium sulfate decahydrate ata temperature below 30° C.

The mother liquor is now consisted of about 30% of sodium sulfate andabout 10% of taurine, along with various percentages of sodiumditaurinate and sodium tritaurinate. This solution is concentrated toabout one half to one third of its original volume in an evaporativecrystallizer, at a temperature from 70 to 95° C., preferably 75 to 85°C., to yield a suspension of sodium sulfate, which is removed byfiltration at the same temperature. The temperature is kept high enoughto prevent the crystallization of taurine at this stage.

The filtration mother liquor, now saturated with sodium sulfate and richin taurine, is cooled to 33-35° C. in the 1^(st) cooling crystallizer tocrystallize the second crop of crude taurine.

The cycle of evaporative crystallization at higher temperature,preferably from 75 to 85° C., to remove sodium sulfate, and the firstcooling crystallization at lower temperature, preferably at 33-35° C.,can be continued until the solid content of impurities, mainly sodiumditaurinate and sodium tritaurinate, accumulates to about 30% of thesolid content in the mother liquor.

The mother liquor from the first cooling crystallization stage can bereturned to the ammonolysis step. Preferably, the mother liquor iscooled to 10 to 15° C. in the 2^(nd) cooling crystallizer toco-crystallize taurine and sodium sulfate decahydrate, i.e., Glauber'ssalt. The co-crystalline mixture is removed from the mother liquor bycentrifuge and returned to a dissolution and preheat unit for theevaporative crystallization step. It becomes apparent from FIG. 2 thatlower temperature may be used, but excessive cooling is required to beeconomical. At higher temperature, removal of sodium sulfate is notcomplete.

The mother liquor from the second cooling crystallization stage isusually comprised of 25-30% of sodium ditaurinate and tritaurinate, 5-7%of taurine, and 7-8% of sodium sulfate. Sodium hydroxide is then addedin an amount sufficient to turn taurine to sodium taurinate, sodiumditaurinate to disodium ditaurinate, and disodium tritaurinate totrisodium tritaurinate. In other words, the molar amount of sodiumhydroxide is equal to, or slightly more than, the molar amount of totaltaurinates in the solution. This solution is then saturated with ammoniato 15 to 28% and returned to the ammonolysis step. Optionally, thissolution may be combined with a new batch of sodium isethionate orsodium vinyl sulfonate for the ammonolysis step.

Some of the mother liquor from the 2^(nd) cooling crystallization needsto be purged from the cycle, when uncharacterized impurities start toadversely influence the quality of the product. The amount of purgesolution in each cycle depends on the quality of starting materials, inparticular, sodium isethionate and sodium vinyl sulfonate. If crudesodium isethionate in the ethylene oxide process is used, purge isrequired in about every five to eight cycles, because ethylene glycol, abyproduct from the reaction of ethylene oxide with water, starts toaccumulate. If sodium isethionate is prepared from ethanol and ethylene,no purge is necessary at all.

Crude taurine obtained in the cyclic process is recrystallized fromdeionized water one or more times to yield a product of pharmaceuticalgrade. The recrystallization mother liquor may be reused several timesuntil it affects the quality of the product obtained. This motherliquor, consisting of residual taurine, sodium sulfate, and impurities,is then sent to dissolution and preheat unit for the evaporativecrystallization.

It should be appreciated that no waste is generated in the cyclicprocess according to the present invention for the production of taurinefrom ethanol and ethylene, because sodium sulfate, discharged in thecyclic process, is recycled continuously to prepare sodium isethionateand sodium vinyl sulfonate.

The process according to the present invention can be carried outdiscontinuously, semi-continuously, and continuously.

EXAMPLES

The following examples will illustrate the practice of this inventionbut are not intended to limit its scope.

Example 1

This example relates to the preparation of sodium ditaurinate and itsreaction with aqueous ammonia under ammonolysis reaction conditions.

Into a 1 L flask, equipped a refluxing condenser, is added 31.5 g (0.30mole) of diethanolamine and 300 mL of dichloroethane, then 51.0 mL ofthionyl chloride. Solid suspension formed immediately after the additionof thionyl chloride and then dissolved upon warming to 50° C. Duringrefluxing, the solid suspension is dissolved and then the crystallinesolid appears. The crystalline suspension is refluxed while beingstirred for 3 hrs. The reaction is quenched by adding 20 mL of methanoland the solvents are removed under vacuum. A white crystalline material,bis(2-chloroethyl)amine hydrochloride, weighted 53.0 g, is obtained in aquantitative yield.

To the flask is added 500 mL of deionized water, 100 g of sodiumsulfite. The solution is stirred at a temperature first at 50-60° C. for3 hrs, then at 95° C. for 4 hrs. HPLC and LC-MS shows completeconversion of the starting material to the desired sodium ditaurinate.

The excess sodium sulfite is destroyed by addition of 40 mL of 30%hydrochloric acid, followed by careful adjustment of pH to 6-7 withsodium carbonate. The solution consists of practically pure sodiumditaurinate and sodium chloride. The solution may be used directly inthe ammonolysis reaction.

To obtain pure sodium ditaurinate, the aqueous solution is vacuum driedto give a white solid. Into the flask is added 600 mL of anhydrousmethanol, and the suspension is refluxed for 30 minutes to dissolvesodium ditaurinate in methanol. After filtration to remove sodiumchloride, the methanol solution is cooled to room temperature tocrystallize pure sodium ditaurinate, which is used as analyticalstandard.

Crude sodium ditaurinate, prepared from 0.30 mole of diethanolamine, isdissolved in 300 mL of water containing 26.0 g of sodium hydroxide. Thesolution is then mixed with 600 mL of 25% aqueous ammonia and heated inan autoclave at 220° C. for 2 hrs.

HPLC analysis of the reaction solution shows the formation of sodiumtaurinate (74%), sodium ditaurinate (24%), and sodium tritaurinate (2%)on the molar basis.

Example 2

This example relates to the preparation of sodium tritaurinate and itsreaction with aqueous ammonia under ammonolysis reaction conditions.

Into a 1 L flask, equipped with a refluxing condenser, is added 29.8 g(0.20 mole) of triethanolamine, 300 mL of dichloroethane, then 51.0 mLof thionyl chloride. The mixture is heated to reflux for 4 hrs. Thereaction is quenched by adding 20 mL of methanol. Removal of solventgives a white crystalline mass of tris(2-chloroethylamine) hydrochloridein quantitative yield.

To the flask is added 500 mL of deionized water, 100 g of sodiumsulfite. An oil phase is separated first. After heating at 60° C. for 2hrs and 98° C. for 5 hrs, the oil phase disappears and a clear solutionis obtained. HPLC and LC-MS shows complete conversion of the startingmaterial to the desired sodium tritaurinate.

The crude reaction solution is transferred to a 2 L autoclave, to which26 g of sodium hydroxide and 600 mL of 25% aqueous ammonia are added.The autoclave is heated to 220° C. for 2 hrs to carry out theammonolysis reaction.

HPLC and LC-MS analysis shows that sodium tritaurinate is converted to amixture of sodium taurinate (72%), sodium ditaurinate (23%), and sodiumtritaurinate (5%) on the molar basis.

Example 3

This example demonstrates the conversion of sodium ditaurinate andsodium tritaurinate in the recrystallization mother liquor to sodiumtaurinate.

To 200 mL of the mother liquor from 2^(nd) cooling crystallizationstage, composed of sodium ditaurinate (25% by wt), sodium tritaurinate(3% by wt), taurine (5% by wt), and sodium sulfate (6% by wt), is added15 g of sodium hydroxide, 500 mL of 25% aqueous ammonia. The solution isheated in a 2 L autoclave at 220° C. for 2 hrs to carry out theammonolysis reaction.

HPLC and LC-MS analysis shows that the reaction solution is comprised ofthe following taurinates: sodium taurinate (76%), sodium ditaurinate(21%), and sodium tritaurinate (3%) on the molar basis.

Example 4

This example is directed to a process for the separation of taurine fromsodium sulfate and from sodium ditaurinate and sodium tritaurinate.

A starting solution is prepared by first boiling the solution from theammonolysis reaction to remove excess ammonia, and then adding enoughsulfuric acid to pH 5-7. The solution is consisted of 30% taurine, 26%sodium sulfate, and 7% sodium di- and tri-taurinates.

2000 g of the starting solution is cooled from 80° C. to 33° C. to forma slurry consisting essentially of the first crop of crystallizedtaurine, which is separated by filtration at 33° C. and washed with 100g of cold water. The recovered taurine is dried and weighed 398 g.

The separated mother liquor, weighed 1580 g, is boiled to evaporate to900 g to form a slurry of sodium sulfate. This slurry is cooled to 80°C. and filtered to recover sodium sulfate, weighed 304 g.

The mother liquor, containing 202 g of taurine and 216 g of sodiumsulfate, is cooled to 33° C. to form a second slurry of taurine. Afterfiltration and washing with cold water, 124 g of taurine is obtained.

The mother liquor from the previous step, now containing 78 of taurineand 216 g of sodium sulfate, is cooled to 10° C. in 2 hrs to obtainslurry of taurine and Glauber's salt. The crystalline solid is obtainedas a mixture of taurine and sodium sulfate decahydrate.

This final mother liquor, about 500 g, is consisted of sodiumditaurinate and tritaurinate (28%, 140 g), taurine (24 g, 4.8%), andsodium sulfate (35 g, 7%). This solution is used for the ammonolysisreaction.

It will be understood that the foregoing examples, explanation, drawingsare for illustrative purposes only and that in view of the instantdisclosure various modifications of the present invention will beself-evident to those skilled in the art and are to be included withinthe spirit and purview of this application and the scope of the appendedclaims.

What is claimed is:
 1. A process for the production of taurine fromalkali ditaurinate or alkali tritaurinate, or their mixture, comprising,(a) adding an alkali hydroxide to a solution of alkali ditaurinate, oralkali tritaurinate or their mixture, to prepare a solution of dialkaliditaurinate, or trialkali tritauriante or their mixture, (b) adding anexcess amount of ammonia to a solution of dialkali ditaurinate, ordialkali tritaurinate, or their mixture, and subjecting the solution toammonolysis reaction to yield a mixture of alkali taurinates, (c)removing excess ammonia from (b) and neutralizing alkali taurinates withan acid to form a crystalline suspension of taurine, and (d) recoveringtaurine by means of solid-liquid separation.
 2. The process according toclaim 1, wherein alkali ditaurinate and alkali tritaurinate are preparedfrom diethanolamine and triethanolamine, respectively.
 3. The processaccording to claim 1, wherein alkali ditaurinate, alkali tritaurinate,and their mixture are the byproducts in the production of taurine by theammonolysis reaction of alkali isethionate or alkali vinyl sulfonate. 4.The process according to claim 1, wherein the catalysts for theammonolysis reaction are sodium hydroxide, potassium hydroxide, lithiumhydroxide, sodium carbonate, potassium carbonate, lithium carbonate,sodium sulfate, sodium sulfite, potassium sulfate, and potassiumsulfite.
 5. The process according to claim 1, wherein alkali metals arelithium, sodium, and potassium.
 6. The process according to claim 1,wherein the acids are sulfuric acid, hydrochloric acid, nitric acid,hydrobromic acid, sulfurous acid, sulfur dioxide, and carbon dioxide. 7.The process according to claim 1, wherein the ammonolysis reaction iscarried out at a temperature from 150 to 280° C. and under a pressurefrom autogenous to 260 bar.
 8. A cyclic process for the production oftaurine from alkali ditaurinate, alkali tritaurinate, and alkaliisethionate in an overall molar yield of at least 85% as calculated fromthe molar mass of alkali isethionate, comprising: (a) adding excessammonia to a solution comprised of alkali isethionate and subjecting thesolution to ammonolysis, (b) removing excess ammonia from the solutionof step (a), neutralizing the solution with an acid to form taurine, andseparating the taurine to yield a mother liquor solution comprised ofalkali ditaurinate and alkali tritaurinate, (c) adding an alkalihydroxide to the mother liquor solution of step (b) comprised of alkaliditaurinate and alkali tritaurinate to prepare a solution comprised ofdialkali ditaurinate and trialkali tritaurinate, wherein the molaramount of the alkali hydroxide is at least equal to the molar amount oftotal taurinates in the mother liquor solution of step (b); (d) addingexcess ammonia to the solution comprised of the dialkali ditaurinate andtrialkali tritaurinate, and subjecting the solution to ammonolysis, (e)removing excess ammonia from the solution of step (d) and neutralizingthe solution with an acid to form a crystalline suspension of taurine,and (f) recovering taurine by means of solid-liquid separation to obtaina mother liquor solution comprised of alkali ditaurinate and alkalitritaurinate.
 9. The cyclic process according to claim 8, wherein thealkali metals are lithium, sodium, or potassium.
 10. The cyclic processaccording to claim 8, wherein the acid is selected from the groupconsisting of sulfuric acid, hydrochloric acid, nitric acid, hydrobromicacid, sulfurous acid, sulfur dioxide, and carbon dioxide.
 11. The cyclicprocess according to claim 8, wherein the ammonolysis reaction iscarried out at a temperature from 150 to 280° C. and under a pressurefrom autogenous to 260 bar.
 12. The cyclic process according to claim 8,wherein the mother liquor solution comprised of alkali ditaurinate andalkali tritaurinate in step (c) further comprises added alkaliisethionate.
 13. The cyclic process according to claim 8, furthercomprising adding an alkali hydroxide to the mother liquor solution ofstep (f) comprised of alkali ditaurinate and dialkali tritaurinate toprepare a solution comprised of alkali tritaurinate and trialkalitritaurinate, wherein the molar amount of the alkali hydroxide is atleast equal to the molar amount of total taurinates comprised of thealkali ditaurinate and alkali tritaurinate, and recycling the solutionto the ammonolysis in step (a).